Slot contents can be accessed with the standard MediaWiki API:Query as follows:

api.php?action=query&format=json&prop=revisions&titles=Test%20page&rvprop=content&rvslots=*

Additionally a Visualdata query can be performed using the following api:

api.php?action=visualdataquery&format=json&schema=Book&query=%5B%5Btitle%3A%3A%2B%5D%5D&printouts=title%7Cauthors%7Cdate&limit=500&offet=0&order=date desc

which contains the following parameters:

Note that the query parameter can also contain an article id or page title (without enclosing it in square brackets) in order to retrieve the data related to a specific page.

The query result is returned in json format and it is responsibility of the consumer application to format it as needed.